Until shortly after Patch 2.3.2, Grimtotem Spirit Guides were the only tamable Spirit wolves. The bizarre appearance of the wolf, in addition to its unusual taming method, had made some people suspicious that the Grimtotem Spirit Guide was not intended to be tamed and would be removed as a potential pet. Although a post from a Blizzard Poster, Issuntril, claimed that Grimtotem Spirit Guides would be left tamable, [1] the ability to tame them was removed in a hotfix as of 1/14/2008. [2]

The reason for the Spirit Guide's removal is that Blizzard felt that the "Undead appearance did not fit with the Hunter class." Considering that there are several other mobs that also look Undead, but are still tameable (notably, the Plagued Swine and Diseased Black Bears of the Plaguelands, and the Bears and Wolves in Felwood), the removal of the Spirit Guide is inconsistent with the reason for its removal.

It was later returned to the game as Grimtotem Spirit Wolf, an untameable version of the Grimtotem Spirit Guide.

They despawn 7.5 seconds after they appear, so it's impossible to tame without special items/abilities, as taming lasts 20.0 seconds. Some items and abilities that can help you tame this elusive wolf are:

Mystical Skyfire Diamond: Cuts the next spell cast time in half. This is a must for reducing the cast time from 20 seconds to 10 seconds. Note that this can be procced by repeatedly changing aspects.